1. Field of the Invention
The present invention relates to a device and method for protecting a tool such as a measuring instrument (probe) or a specialized working tool in a well, this tool being fixed to the end of a drill string.
2. Description of the Prior Art
In the devices and methods of the prior art, the tool or instrument is caused to leave its protective casing or jacket by a movement of the tool or instrument relatively to the drill string and to the casing, the casing being fixed relative to the drill string.
Such an operating mode has numerous drawbacks. In fact, very often the specialized tools, such as well logging probes, require an electric connection with the surface of the well. This connection is generally provided by a cable and it therefore advisable to provide members which ensure the electric continuity of the connection during movement of the tool. Such members are particularly fragile and present difficulties in use.
Moreover, very often, the devices of the prior art move the tool by pumping liquid inside a hollow string. This results in violently propelling the probe with the risks of damage thereto, particularly if the well is obstructed.
The prior art may be illustrated by the French Pat. No. FR-A-2 547 861, European Pat. No. EP-A-0 122 839 and the U.S. Pat. No. 4,349,072.
The present invention overcomes these drawbacks by providing a retractable protective device for a specialized instrument or tool working in a well, this tool or instrument being fixed to the end of a drill string.